Yeah; telephone numbers and sending email addresses can be spoofed / failed / forged. (IP addresses can be spoofed too, but that isn’t relevant in this case.)
Contact your cellular carrier, and contact a lawyer or local police if either are an option, as this reported behavior may be considered a form of harassment depending on local laws. Your carrier may have options, or an interest in the spoofing.
If the person is consistently using specific words or phrases, the Bouncer app can mask those messages.
More generally, and it won’t prevent the SMS messages from arriving, mute all unknown senders to reduce the disruptions: Block, filter, and report messages on iPhone - Apple Support