I’ve never had anyone tell me operations with the same priority can be done either way, it’s always been left to right

It's left to right within each operator. You can do multiplication first and division next, or the other way around, as long as you do each operator left to right. Having said that, you also can do the whole group of equal precedence operators left to right - because you're still preserving left to right for each of the two operators - so you can do multiplication and division left to right at the same time, because they have equal precedence.

Having said that, it's an actual rule for division, but optional for the rest. The actual rule is you have to preserve left-associativity - i.e. a number is associated with the sign to the left of it - and going left to right is an easy way to do that.