Can you help me understand this part "new RSA(buff.slice(22"?

[hugomosh]

I am writing the library to work on React Native, I have come to the part to encrypt the WiFi password. Can you explain me why it takes the 21 first bits? of the public Key?
First time using encryption.

SoftAP.prototype.publicKey = function publicKey(cb) {
	is(cb);
	this.__sendCommand({ name: 'public-key' }, function response(err, dat) {
		checkResponse(err, dat, cb);
		var buff = new Buffer(dat.b, 'hex');
		this.__publicKey = new RSA(buff.slice(22), 'pkcs1-public-der', {
			encryptionScheme: 'pkcs1'
		});
		cb(null, this.__publicKey.exportKey('pkcs8-public'));
	}.bind(this));
};

Thanks