Yes this could be the reason. If I understand correctly, the chip has a VDDH pin which allows direct battery connection and saves the external LDO.
Unfortunately we have to live with the external LDO on Seeed board since VDD only tolerates up to 3.6V. We may connect non-rechargeable Lithium battery directly to VDD but we cannot avoid, if it exists, reverse leakage to the LDO.