Yep, rowers seem to breed deceptively strong types too.
I remember doing a session next to a Sri-Lankan looking girl a few years ago. There was hardly anything of her but she was really giving it some. IIRC I was one setting below her but could only pull at maybe 80% of her pace. I did my usual distance for 10 mins and left her to it.
The weirdest occasion was seeing a really unkempt (and I mean genuinely tramp-like) bloke spend 40 mins going absolutely flat out. Only saw him that once and that was the only piece of kit he used. Was a bit odd.