What the literature definitely finds is that CBD ratio is crucial for anxiety (higher CBD = less anxiety). Some of the first lab experiments were pure THC and quite intense/unpleasant relative to what you'd get from a plant naturally "full spectrum." If you're ever in california, NY, Maryland, whatever then try something with 1:1 THC:CBD and maybe get some of the other CBs in there too.

[Strain sativa/indica can sort of be an indicator, but going by the dose of each active ingredient is the more scientific approach]

The entire field of statistics is based off not making critical type 1/2 errors (which meta studies are not able to control well) so I would say it is not just his "gut" feeling.

Agreed. Blending in CBD and other cannabinoids is way more effective than relying on strains. Basically everything out there is extremely high in THC and nothing else. Mixing in high CBD flower reduces anxiety a lot for me

For clean weed - not laced with anything - sativas are more prone to causing anxiety. I doubt one will find any kind of study proving this, it is anecdotal - myself, friends and the internet at large.

While not universally true, it seems that many of the sativas for sale are very high THC which probably is a primary factor. Other factors are terpenes, though there is still a lot of debate on whether it these are real or imagined effects.

Moderate THC (15-20%) indica or indica dominant hybrid flower, using a flower vape, IMHO, is the best way to go. Always a good idea to read strain reviews prior to purchase (or growing) as people will note those that have caused them to be anxious, sleepy, hungry, horny, etc.

People can also have very different reactions when taking a drug (weed, shrooms, lsd, etc) alone vs with friends, something to consider as well.