Is it considered to be within "lnormal" reactions for someone to have mild cramping the day after urodynamics or is it a reason for concern?

Probably Normal. After any procedure, some mild discomfort/cramping is normal... If becomes prolonged or severe should follow up with md.
Can be normal. Mild cramping may be expected. The test stretches the bladder to "test it's limits". Check with your urologist if it does not resolve quickly.