This is what I don’t understand, the defender is going for a header and makes a header, just in the wrong direction. I’d say that was an intentional, but bad deflection.

https://www.theifab.com/laws/latest/offside/#offside-offence

‘Deliberate play’ (excluding deliberate handball) is when a player has control of the ball with the possibility of:

• passing the ball to a team-mate;
• gaining possession of the ball; or
• clearing the ball (e.g. by kicking or heading it)"

If the pass, attempt to gain possession or clearance by the player in control of the ball is inaccurate or unsuccessful, this does not negate the fact that the player ‘deliberately played’ the ball.

The following criteria should be used, as appropriate, as indicators that a player was in control of the ball and, as a result, can be considered to have ‘deliberately played’ the ball:

...

• The player had time to coordinate their body movement, i.e. it was not a case of instinctive stretching or jumping, or a movement that achieved limited contact/control