The assignment problem constraint $x_{31}+x_{32}+x_{33}+x_{34}2$ means:

agents $1,2,3,$ and $4$ can be assigned up to $2$ tasks.

a mixture of agents $1,2,3$ and $4$ will be assigned to tasks.

agent $3$ can be assigned to no more than $2$ tasks.

agent $3$ can be assigned to $2$ tasks.