My question is, isn't there a difference between an employer contribution to a solo 401k or an employee contribution to a solo 401k?
it depends on what you're driving at
an employee 401k contribution reduces line 1 of their w-2 but the gross amount of wages is a deduction for the partnership. (any employer match goes on line 18)
instructions for line 18 of 1065 - retirement plans.
Line 18. Retirement Plans, etc.
Do not deduct payments for partners to retirement or deferred compensation plans including IRAs, qualified plans, and simplified employee pension (SEP) and SIMPLE IRA plans on this line. These amounts are reported in box 13 of Schedule K-1, using code R, and are deducted by the partners on their own returns.
