Downturn in energy combined with Trump's immigration policies. Most of our net inbound immigration has been international for some time.
I found the second sentence of your quote curious then realized what it meant and tuned in. I recall in the early 1980's before Oklahoma's S & L and energy crash seeing so many car tags from other states on a regular basis as recent transplants to Tulsa due to a blazing oil industry for which Tulsa was a major hub at the time. Along with that, American Airlines brought quite a few managerial and operations employees from White Plains in the 1970's. The oil business attracted many people from all over the country in those days. Tulsa sort of pre-dated Austin when it came to an industry or a few industries causing thousands to flock to a metro every year. The sh1tty economy all over the U.S. in the early '80's that Tulsa had managed to avoid until the Penn Square collapse in 1982 and finally oil plummeting to $9-10/bbl in 1986 drove people to our doorstep until 1984 or 1985. I think Tulsa would be seeing better growth had the oil industry not decided making Houston the center pivot of petroleum was essential.
As to the first sentence: Trump's immigration policies probably have less to do with any impact on the Tulsa area than OK HB 1804 from 2007 did. I distinctly remember after HB 1804 passed, documented Mexicans that worked for us ended up leaving the state as they were afraid of being rounded up even though they had the proper visa and documentation.
I've not studied immigration trends since Trump took office but I'd be surprised if we have a much better handle on illegal southern border crossings than we did 20 years ago. He talks tough because he knows his power-base wants to hear him talk about how successful we are at keeping illegal crossings to a minimum but there's plenty of anecdotal evidence out there that it's still pretty easy to slip into the southern U.S. from Mexico.