I can tell straight away if someone is playing a tune in our session that they learned from dots.

Even when it's the same player, and an experienced one?

I doubt you could tell which of the tunes I play I learned each way. Mostly I don't remember.

There are a lot of tunes I picked up using both dots and live or recorded performance, using both before trying to play it myself, and either might have come first. Think you could categorize those from hearing how I play them?

People who make Steve's claim are usually comparing apples and staplers. There are players who turn up at sessions for the first time having learned all their stuff from notation. Of course they sound different. They sound different because they don't have much experience.

You can sometimes tell when somebody's learnt from a particular recording - particularly when the tempo on the recording is odd. Most people in Scotland play "Miss Gordon of Gight" at a funereal pace because Alasdair Fraser did it that way, and they learned it from Fraser's recording, directly or otherwise - if, like me, you got it directly from the 18th century print source before Fraser recorded it, you're more likely to put some energy into it (hint: it's a reel, and there is a reason why it should go as fast as possible).