Christianity started out wrong in its understanding about the nature of God and what necessary to achieve "enlightenment".
This reflects a human view as to what the 'understanding about the nature of God and achieving either enlightenment nor salvation in reality is.
What was the Buddha wrong about?
Like all religions and religious beliefs being right or wrong is not likely the bottom line, Considering the fallible nature of human view it is likely that any one religion or religious belief is limited and in some way flawed as to what the universal reality is beyond individual human beliefs,
Christian thinking has evolved away from its roots. Especially when it comes to universalists. I'm not saying this is wrong, just that it had to or has changed from its origins.
Likely true, but considering the fallible nature of humans Buddhism in its many variations may have evolved away from its roots. In fact in many ways I 'believe, it has. I believe the prevalence of ritual, imagery and statues, and clinging to asceticism and traditions are variations of Buddhism that may be evolved away from its roots.
The attempts of universalists to remove the human shroud chained to the human images of the Divine may be closer to reality than the orthodox view of Christianity, but again all views are likely flawed.
So maybe we see similarities not because of what Christianity was but because of what it has become.
It is possible both may be a limited extent true,
Maybe they both talk about some state of human perfection but how they go about it is completely different.
They being human going about things being different is normal and flawed.
Christianity is about the appeasement of a God.
Possibly not the intent of Christ,
Buddhism is about letting go of attachment to impermanence.
Actually in the rejection of materialism in Christianity also may acknowledge the need to let go and the nature of impermanence of our existence.
Folks can try to make Christianity into something it's not out of a desire to hold on to their cultural beliefs but a some point, maybe it's just time to let go.
I believe it is the nature of fallible humans in history to make religions into something that they are not intended, The apparent cultural burden on both Buddhism and Christianity is a classic example. Also the vain efforts to define or undefine what the Source some call Gods and others nothing is likely human efforts to define what cannot be defined.