What an idiot, apart from the obvious safety concerns for child and home, the dick doesn't know what the hell he's talking about, triacs don't have source/drain terminals
^ This. That is a FET. All the fool modifying the blanket has done is remove the solid-state switching that was keeping it regulated.
It's now on full, all the time, because that switching was removed.
The device hopefully meets CE standards and likely has at minimum an NTC somewhere in it, but that doesn't stop the child-roasting blanket from roasting until then
I do electronics repair for a living. The Venn diagram of "short-circuits safety features" and "total idiot" is usually a circle