You didn't boil the hops to sanitize? Infected & ruined. Kidding.
One possible explanation for "restarting fermentation" is simply the release of CO2. The fine particles of pellet hops act as nucleation sites and can cause fizzing & release of residual CO2. So if you didn't degas your first hydrometer sample, it's possible it was propped up a few points by the bubbles; so now, this new sample with reduced CO2 content reads lower.
Interesting theory. I could accept that. That does make it tough to determine if I'm at FG after dry hopping, though. Maybe I'll take another reading as soon as I get home and then crash it and try to get in a bottle session tomorrow night. Is a 27 hour cold crash worth it?
Definitely do not want to risk bottle bombs. We have a unique living situation, as well as an 18 month old. Aside from the physical risk, I have a feeling that SWMBO might try to put an end to this hobby if that happens. No room to keg unfortunately.