He wants to give those posts exposure by posting them on his blog, so a second blog would counteract that. What he should do is put “Guest post: ” in front of each title.

The very first line reads "This is a guest post by Karthik C. S., Amit Sahai, and Jie Xue." That seems sufficient.

Experience has demonstrated that it's not sufficient!

What would also lessen the confusion would be people putting in the effort to read a little further than the headline before coming up with a hot take.

People have disclaimer blindness. it's similar to sidebar or banner blindness. it is also possible it does not show up well on mobile devices. how many people read fine print or terms of service?

That's a charitable view point.