The joint procurement document refutes the claim that an offer of 50,000 ventilators was made to the UK Government by the European Union.
However, the EU procurement process involves each member states to place orders individually and the suppliers will negotiate the quantities and deadlines for deliveries of the equipment. Therefore the Commission itself does not offer the ventilators. This implies that Boris Johnson has not turned down an offer of 50,000 ventilators as the negotiations are made between the individual suppliers and the respective governments.
The COVID-19 pandemic has given rise to a lot of potentially dangerous misinformation. For reliable advice on COVID-19 including symptoms, prevention and available treatment, please refer to the World Health Organisation or your national healthcare authority.