I know this will sound like my club bias is coming into play, but I don't think this was as clear cut as it looked on first viewing.
Hear me out.
When you watch the footage closely, you will see that Holding's arm bounces off Iheancho's face which then causes Holding's arm to hit the ball. What are you supposed to do in that situation? Had that not happened, the ball wouldn't have touched Holding's arm. As you don't naturally jump up with your hands by your side, he's obviously tried to gain some 'spring' in his jump by using his arms. However, I wouldn't have complained if a penalty was given. When I saw it in real time, it was a stonewall penalty. Especially in this day and age, when your hands are that high, you always run the risk of giving a penalty away.
Think I'm just making excuses? It isn't just me who was saying this.
From FoxesTalk (A Leicester City fan forum):
Captain:
"He [the ref] got it right, Ndidi headed The defenders arm on to the ball, if Wilf hadn’t been there he would have headed the ball away cleanly. I thought that on first viewing and the analysis on my stream agreed with me.
I actually thought the ref was alright a little on the lenient side, but he was the same for both teams and didn’t let the Arsenal players whinging get to him."
The Horse's Mouth:
"...with the penalty shout, Ndidi does push his arm into it. Can't say it was a penalty tbh. It's a shame, because first half we could have had 3 or 4 but couldn't bury our chances. Tbh, I think for West Ham I'd drop Vardy for Kelechi and have Madders in behind. Playing all three just doesn't work"
Source:
https://www.foxestalk.co.uk/topic/117231-arsenal-post-match/?page=12
When you have Leicester fans, by their own admission, saying they don't think it was a penalty, I think it suggests the incident wasn't so cut and dry.