"The couple, who are both students at Utah State University in Logan, got married in August and the math problem brain freeze happened just before Christmas. He posted the video on YouTube back in December to share with their family and friends. The video had been sitting there, undiscovered for months, and neither one of them expected it to go viral.** [italics mine]

""I honestly had no clue what to think," she said about finding out millions had watched her video. "At first I was shocked and then really mad. … Definitely, it was a roller coaster for a while. My emotions were pretty intense."

"What YouTubers didn't see, they say, is that Chelsea had been up all night studying for finals the night before and that her brain was completely fried. Plus, they had no radio on the boring car ride to visit her family in Boise and had to keep one another entertained."

Excerpt above is from this article

More excerpts:

Travis Chambers told "Good Morning America" he made with video with no mal intent and that it was nothing more than "affectionate teasing."

"I asked the question and she started answering and I said, 'I have to film this. Her family is going to think this is so funny,'" he explained today. "It was just so funny to me. We were just kind of goofing off, driving home. I think it looks a little worse than it was. …We tease and joke a lot.
..........

Along with millions of views, the video has racked up a lot of comments, with many wondering whether the husband is in hot water with his spouse.

"I was like, 'How could you do this to me?' I was pretty upset, but I realize that our marriage is deeper than that. I can't let this little thing affect how I feel about my husband," she said. "I love him and our relationship has just kind of grown from this."

Her husband does apologize though for any hurt he might have caused his spouse.

"I definitely do apologize to Chelsea for teasing a little bit," he said today. "I'm sorry for the emotional roller coaster it's put you through. I am glad that you are understanding and such a sweet wife and that we are doing well."

**Explanation for its sudden popularity here:
"Even though the video was posted three months ago, "The Real Meaning of MPH" has seen a spike in traffic over the last three days since it was posted on the Tosh.0 blog, which is an Internet companion to comedian Daniel Tosh's Comedy Central show, Tosh.0."

There is also now a comment (from the clip's uploader) under the YouTube clip (BTW, further comment has been disabled) that was not there yesterday:
"Thank you for those of you that have been understanding, positive and supportive through the experience of the unplanned, unintended, and unsought public attention we've received for the viral YouTube video. For those of you that have misinterpreted the context of the video and commented negatively, not having the background story, we sympathize with you, we aren't angry and hope you'll reconsider your feelings. Our relationship has been strengthened by this experience and we encourage anyone with questions to view Good Morning America and our future posts. We're not exactly sure where we will go with the public attention yet but we welcome suggestions. We certainly never wanted to become notorious but when life gives you rotten cabbage sometimes you just might be able to make lemonade :) We have created a Page on Facebook, 'Travis and Chelsea Chambers' Much love, Travis and Chelsea"

Methinks this all explains a LOT!
For one thing, it sounds to me like she was already aware of the clip -- and OK with it (but not expecting others besides family & friends to see it).

Actually, I'm impressed. They seem like a pretty solid couple to me, and to have reacted pretty well to what must have been a bewildering, meteoric journey to sudden fame/criticism/humiliation. Although I still think he owes her... bigtime! [g]