You most likely took your test on A36 plate, possibly A572, but A572 is more expensive, so why would the lab pay the extra money for test plates.
Hydrogen is not a major problem if you use FCAW electrode unless it was very old. Who supplied the welding equipment and the electrode? I ask because I stopped providing the welder machine and the electrode long ago. Most welders have their own machine and their favorite electrode, so why waste my space and money to see the equipment collect dust.
If the electrode has been sitting around unwrapped or has been left on the machine for a period of days it can pick up moisture. However, A36 is very accommodating and not particularly susceptible to hydrogen cracking. The high strength low alloy steels are more susceptible to delayed cracking when the joints are highly restrained, and the quenched and tempered steels are even more so. Again, I doubt the lab is providing the later because of the cost involved.
The laboratory is doing you a favor by keeping it in an oven for several days. The process is called “aging” and it is permitted (not required) by AWS D1.1. Most laboratories don’t bother aging the samples unless hydrogen is a concern and the sample is to be tensile tested. The elevated temperature allows any diffusible hydrogen time to escape before subjecting the test piece to destructive tests.
Best regards - Al