After taking a closer look at the link you provided as well as searching for further information, there does not seem to be anything that directly addresses whether the state's contribution to the 529 plan would be taxable income on your Federal return. Unless you receive a tax document such as a Form 1099-MISC reporting the amount that was received, do not include it as income on your Federal return.
It also does not appear to be considered to be taxable income on your Maryland return. However, if you do receive the state contribution amount, then you cannot claim the deduction on your Maryland return for your contributions to the 529 plan.
@Murt
@SKjames
Given the additional information shared by user Murt, I see I may have misunderstood your original question regarding the state contribution. Hopefully, this answer will provide you with further insight.
[edited 3/19/2022 | 1:02 pm PST]
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