The Spaniard jumped from the bench to score twice for the 2-0 win.
He said at the final whistle: "He (manager Mikel Arteta) told me to come in as a striker this morning. We were talking about it a little bit with one of the assistants. It is the first time in my career that I've played that position.
"He told me to go with my strengths and luckily I could help the team with two goals today."
On him starting as a striker regularly, Merino shrugged: "I don't think so to be honest. It is the first time I have scored a brace coming off the bench as a striker.
"I forgot to give my wife something for Valentine's Day so this goes to her. I think she will appreciate this more than a rose and some chocolate.
"Today was a tough game. But I think these games are the ones you need the spirit. Games like today are really good for the squad."
On Ethan Nwaneri, he added: "He is an amazing player. Every time I do an interview you guys ask me about him.
"We have to keep the foot on the gas and if we keep doing this job then good things will come in the future."