The Qur'an reports the opponents' words:
أَهَٰذَا الَّذِي يَذْكُرُ آلِهَتَكُمْ
“Is this the one who mentions your gods?” (Al-Anbiyāʾ 21:36)
In their hostile speech about the Prophet ﷺ, «هٰذا» carries an implication of contempt and belittlement. The wording treats the person under discussion as unworthy of regard. It is the opponents' disparaging attitude being reported, not a divine endorsement of it.
The demonstrative «هٰذا» is not intrinsically an insult. The scorn arises from the hostile context and the speakers' intention.