The idea of pressing with the thumb on one side of the deck to cause a break to open on the opposite side under reversed cards is commonly attributed to Lin Searles; e.g., Maxwell's The Classic Magic of Larry Jennings, 1986, p. 19. While this attribution has not been contested, an original source for it has not come to light.
The parentage of this idea can be seen in a method for ascertaining the location for a controlled cut of the deck, described in S. W. Erdnase's Expert at the Card Table, 1902, p. 50. The principle employed is the same: using opposing bridges to rock open a break.
Lin Searles did publish another method for using a reversed card or cards to form a break. This was called “The Reverse Autobreak” in a trick titled “The Repeat Pick” in Ibidem, No. 24, Dec. 1961, p. 23. He used the right fingertips to press on the ends of the deck to open a break at the fingers' side of the pack. To date the technique described in Ibidem, Searles later cited a letter he had written in 1957 to Neal Elias. See Pallbearers Review, Eighth Folio, Autumn 1973, p. 667. The dynamic of this technique, though, is different from that of using a simple pressure of the thumb.