Are the primary rear brakes drum or disc on this rig?
Any steps taken to keep the hose off the exhaust?
Air in the lines most often will lead to a softer, more squishy feeling brake pedal as the air is compressible. As
@Malleus said, if the 2nd pedal push feels firmer then you may have been able to apply it quickly enough that the air is still compressed by the first pedal push, thus leading to a better pedal feel the 2nd time around.
Pumping brakes and having them be firmer on the 2nd push can also point to poorly adjusted brake shoes (if you have drum primaries out back) or pads that have gotten pushed out to far. Timing can be a relevant factor in feeling what may be causing the extra pedal pushes to feel better. A quick 2nd push that feels better may mean that the first push moved the shoes against the drums, and/or pads against the rotors, and then the 2nd push of the pedal was quick enough to be applied before the shoes/pads retracted.
If follow up pedal pushes feel good during a longer period until you turn, hit a bump or something like that then it could point to pads getting pushed out on one/more wheel. If you are running 4 wheel disc brakes for your primary braking then the likelihood of loose pads that need to be pushed in with a 1st pedal push is pretty low in your situation but definitely still possible. Some potential causes of this can be loose wheel bearings or other slop that allows the pads to be pushed away from the rotors more than they should be as you drive. It may be worth lifting each wheel on your rig and confirming that there's no excess slack before you drive the 80 too much, just to be safe. I've seen wheels fall off, etc. on vehicles that were recently serviced by a shop...
If you are running drum brake primaries in the rear then I'd say the likelihood of them being setup too slack is high but very easy to fix. You can typically lift one end of the axle, remove the wheel and then access the adjuster and set the shoe clearances. The shoes should auto adjust on an early 90s Toyota so there may be issues with the assembly inside the drum and I'd personally give things a look over but that's a guess as I've not worked on 90s landcruiser drum brakes.
Your parking brakes are drums on the rear even if you have 4 wheel disc brakes. I'm sure that your parking brake shoes need to be adjusted closer to the drum. You can lift the axle then remove the wheel to access/set the brakes. All you need from that point is a flat head screw driver and the knowledge of which hole to stick it in and how to wiggle it to adjust the brakes. We can share info on that, or you can find it on the forum, if you want to do this yourself. It's a quick adjustment if you are familiar with it but may take a little while the first time. I run the parking brake adjustment pretty far out to snug the shoes down and then ease it off until it barely rubs on wheel rotation. I basically leave it as tight as I can without it generating excess heat/resistance while the 80 is rolling.
As said above, it seems pretty clear that they didn't do the work properly. Brake shoe adjustment, fluid flush and general inspection would be the likely next steps if this were my 80.