I found a web site that said he had sold it to Biglari Holdings for $4.2m in 2010, before (as we both noted) buying it back. (in 2013 for $1.7m)

Yeah, basically Biglari Capital, as the GP, also contained his entire net worth at the time - the GP's share of the Lion Funds from all of the performance allocations since he started those funds. The GP was sold for $1 but the capital account was transferred to the Holding company at its balance that day.

"Pursuant to the Stock Purchase Agreement, Mr. Biglari sold all of the shares of Biglari Capital to the Company for a purchase price of $1.00 plus (i) an amount equal to Biglari Capital’s adjusted capital balance in its capacity as general partner of the Lion Fund, and (ii) an amount equal to the total incentive reallocation allocable to Biglari Capital for the period from January 1, 2010 through April 30, 2010, less any distributions in respect of such amounts previously received by Mr. Biglari. The payments set forth in clauses (i) and (ii) total $4,107."

The narrative that resulted from stuff like that Forbes articles makes it seem like he sold a thing to the company for $4.2m and bought that same thing back for $1.7m and that is not accurate. But it fits nicely with the popular opinion.