He was wrong in adding the fourth Rakah and he should have sit immediately as the extra third Rakah was invalid!

One of my friends is Hafiz and leads Traveh prayer. During Traveh his intention was two rakah but he forgot and got up for third raka. No body behind him pointed out mistake. He realized it at third raka and then completed the forth raka also. After he concluded the prayer with sajda sahv. Will it be considered two raka or four raka? Please clarify?

Prayer | June 30, 2015 4:38 am
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I saw your vedio about witr salah and got to know that it should not be similar to magrib salah.While praying witr i pray the first two rakhas normal and then sit down for tashahud and pray the third rakha and then tashahud and tasleem.but in the third rakha i recite another surah after suratalfatihah and then qunoot which is different from magrib prayer.Is this a right practice?
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If the imam pronounces IHDINAs siratal mustaqeem as IHIDINA adding kasrah to ه does. Does It change the meaning?