Rubbish. A GE can take place 6 weeks after it is called. If Brexit is delayed, the GE could easily take place before Christmas.The GE is one of the reasons that the extension is likely to be a long one.
The reason for the long delay would be the hope the Tory lead in the polls would evaporate.
That would not happen. If the GE is delayed, the current opposition will have to negotiate - which they will rapidly find politically toxic with BoJo gleefully laying into their failure to get a deal.