I think they're both sort of right!
If your lo is sick, or had a rough night or the previous nap was short or something, or even none of those things, then there's no harm in letting them sleep a little extra. If it's A LOT longer than normal, then you do run the risk of messing things up with not eating too much during the day, possibly waking more often at night as a result, etc.
I would suggest looking at it from more of a "pattern" point of view. A one-off is probably no big deal, but if this is happening consistently, then you might need to look more at what else is going on - for instance, should you be stretching out to a 3.5 routine or whatever... HTH!
(And what ended up happening, BTW?)