I think bail norms probably vary by jurisdiction, etc., and your assumptions are not correct.
My guess is he was not required to post full collateral, i.e. the only collateral here is the home, and then Sam, his parents, and two others posted essentially an unsecured guarantee for the full $250M, such that the government could recover up that amount from any assets held by any of those parties. While unsecured, note that the government probably has priority over any creditors and could and would seize any assets of those parties per the guarantee.
My guess is he was not required to post full collateral, i.e. the only collateral here is the home, and then Sam, his parents, and two others posted essentially an unsecured guarantee for the full $250M, such that the government could recover up that amount from any assets held by any of those parties. While unsecured, note that the government probably has priority over any creditors and could and would seize any assets of those parties per the guarantee.