Yeah, the mininuke launcher is a shoulder-fired weapon, not emplaced artillery like the M-29 Davy Crockett - which was a recoilless rifle firing an oversize projectile, not a man-portable spring mortar.
If anything, it would probably look more like this:

Though to be fair, the PIAT used an additional propellant charge to launch its projectile that our mininuke launcher lacks. Adding one could give it a longer range, but it would mean both the launcher and the ammunition would have to be even bigger and heavier, and they’re already pretty massive.