A fire grue has 2 attacks per turn. If you got critted twice, 150 damage in a turn seems perfectly possible. Unlucky, but possible. I'm also pretty sure that the maximum non-crit damage of a fire grue is definitely more than 35.
Also, when judging these things one has to take into account that crits double pre-PV damage, but the effect of PV means that effective damage is more than double.
Example, single hit, 40 damage, 20 PV -> 20 final damage.
Double hit, 40 and 40 damage, 20 PV -> 20+20=40 final damage.
Double crit, 80 and 80 damage, 20 PV -> 60+60=120 final damage.