I'm not entirely sure what you or this technician are talking about... but I'll take a stab.

I have run into this multiple times (actually just ran into it today on one Tundra rear caliper) where the bleeder screws get rusty and won't let you bleed them or flush fluid through them. Usually I just clamp off the brake line, remove the bleeder and take one or two of my assortment of tensioner pins and clean the bleeder screw out.

Another possibility (and one I see a lot, not just on 4Runners) is that one or more of the slide pins of the caliper have rusted/seized; sometimes you can get them loose to clean and lube, other times you just have to replace the caliper bracket and/or entire caliper assembly. It is also possible that the caliper piston is seized, but in the case of a seized caliper piston and/or caliper pin you'll see uneven brake wear and dull/rusty rotors.

I will also say that if you try to compress the pistons with the brake line kinked, it'll make you think their seized (I still do that every now and then when I'm not paying attention after I've removed a caliper for a brake job, particularly the rear ones as a lot of them are easy to kink when you flip them out of the way, lol).