If he had just left it at "considering," this would be a very different conversation. Funding "secured" means that it definitively exists, i.e., there is an actual agreement from some investor(s) to fund the operation.
The only reasonable interpretation of the above tweet, is to qualify the second sentence with the first, i.e he personally is only considering a buy offer and that he is secure in the funding ability of the buyer.
Choosing your interpretation, what he said in the second sentence, clearly contradicts the first sentence in the same tweet. So why are you choosing the clearly inaccurate, as due diligence is now taking place, narrowly legal interpretation of two words, over all the other context that suggests your narrow legal reading of those 2 words are not what could possibly have been meant by him.