Its something of a tradeoff space that is always there you either have things that look the same be implicit (eg is 1 and 10000000 the same type? How about 1 and 1. ? How about 1 and -1?, how about 1 and moo? 1e2 and 1f2?

You can have things be explicit and verbose (have explicit unambiguous identifiers on every value), or you can have things magic and then surprising in something like this.

Rails also made a similar decision to basically auto convert what would be the string true to the Boolean value true in many cases. It's not obviously right or wrong, it's just a choice that has tradeoffs.

I think my own sensibility is that it's actually reasonable for something like yaml to allow you to choose to omit quotes and if you do then it's automatic typing: 1e2 is a number and 1z2 is a string. If you want it to be a string you can put quotes on every value if you want, exactly like you would in json, choosing unquoted for things that are strings is choosing the automatic typing case.

But these other values like y and n being autotyped as bool are suspect autotype behavior to me: even once you've accepted unquoted is autotyped you are more likely to be caught off guard by this than by 0 vs true vs 0z.