When you booked the flights through Expedia, providing that you booked it by asking for a flight from Manchester to JFK – then this would count as a ‘through ticket’.
Although you could have bought the tickets as separate transactions on Expedia, this would be a risky thing to do, since having bought one ticket – when you came to buy the next leg of the flight, seats might no longer be available. But if you did this, then technically you do not have a ‘through ticket’, even if they were purchased within 5 minutes of each other.
To put your mind at ease, you could e-mail Expedia’s Customer Support (via their web page) – and ask whether your booking counts as ‘through ticketing’.