Not commenting on whether this is true or not but only to inform of at least one place where glider pilots are taught that steeper turns are less likely to result in a stall. From Glider Basics - From First Flight to Solo, by Tom Knauff:

"It is very important for you to understand it is extremely difficult, if not impossible, to stall a glider in turns of 30 degrees angle of bank or more." You can find the entire discussion on page 79 of his book, as well as in multiple other locations in the text.

Robert

On Tuesday, August 2, 2016 at 3:22:20 PM UTC-5, Tango Whisky wrote:
Le mardi 2 août 2016 22:07:26 UTC+2, a écritÂ*:
At higher G loading as in steep turns many if not most gliders run out of elevator authority making them difficult if not nearly impossible to stall. Airplanes on the other hand have the propeller wash influencing elevator authority.

If your talking bank angles beyond 60 degrees, maybe. Anything below - absolutely not. That is, if you respect max mass in the seat.
Actually, if you stall a 25+ m ship at 60 deg bank, spin entry is much more violent than at 30 deg bank, and stopping the spin takes significantly more time. I've done that, and I won't do it again.

So, relating to patterns where you probably don't do more than 45 degree banks, your statement is senseless.