Sure, but Trump also wasn't a typical conservative candidate (e.g. he got dead last in my red state's [Utah] primary, and won by plurality instead of majority in 2016). His campaign prompted Evan McMullin to attempt to spoil the election in 2016, he was certainly divisive in 2016. I can absolutely see how that could sway someone who detests Trump (say, enough to attempt an assassination) to donate to their most credible competitor. Sometimes the enemy of your enemy is your friend.

That said, another user has posted evidence that maybe that donation was wrongly reported by the major news agencies. So I'll put it in the category of "plausible" instead of "probable," since it fits with my mental model of someone who claims to be Republican yet attempts to assassinate the Republican nominee for President in the first presidential election they're eligible for.